Assuming I've made up my mind to hold on to a token for many years but after a year this token hit a new ATH what should I do as a newbie? Sell or not sell?
It depends on your target goal. If you're planning to hold a potential coin for the long term, you better set a target goal and if you have reached it, sell. The ATH is the most profitable time to sell so it would be wise to sell your coins and reinvest them when the price of your coin strikes down again. It's like applying the basics which is to buy low and sell high.